This invention relates to an improved dielectric, liquid impregnated, wound roll electrical capacitor and more particularly to wound roll capacitors wherein a high dielectric constant polymer coat is utilized on the edges of the electrode foils at the roll ends or edges.
In the production of electrical capacitors, particularly improved power factor correction capacitors utilizing synthetic resin films, principally polypropylene, as the sole dielectric, there have been a number of deterrent electrical problems. These problems relate to the feature that the capacitors are made up of alternating thin strips of electrode foil and synthetic resin film which are wound together very tightly in a roll form. Then, one or more such rolls are tightly fitted into a casing which is filled with a dielectric fluid to impregnate the roll. Because of the tightness of the assembly and the swelling of the resin film by the fluid impregnant, the usual thin layer of a dielectric fluid at the roll edges between an electrode foil and a film strip becomes markedly thinner. A present practice for other reasons is to use a lower dielectric constant fluid in such capacitors, and when this thin layer of fluid is under a very high voltage stress, breakdown and deleterious corona discharge occurs. This condition limits the development of more efficient and effective capacitors.